Oxime reactivation of RBC acetylcholinesterases for biomonitoring

A low-variability method to reactivate blood cholinesterases (ChEs) after prior exposure of mammals, including humans, to ChE-inhibiting organophosphate esters (OPs) is presented. A concentration of 10 mM pyridine 2-aldoxime methochloride (2-PAM Cl) was incubated with intact red blood cells (RBCs) and assayed virtually free of interfering oxime and hemoglobin (Hb). Variability was decreased by reducing the number of washing steps and sedimenting RBC ghosts through a 7% sucrose cushion. Statistically significant detections of reactivations as low as 5% with average "false positives" of 3.8% were achieved. Relative rates and extent of reactivation after OP treatment of rabbit RBC AChE in vitro were of the order dimethyl- (DDVP) > diethyl- (ethyl paraoxon) >, diisopropyl-substituted (diisopropyl fluorophosphate; DFP) OPs. Rabbit RBC AChE was reactivatable for up to 60 h following dermal exposure to ethyl parathion and reactivatable for only 12 to 24 h following exposure to methyl parathion. Reactivation of plasma ChEs with 0.1 mM 2-PAM Cl in the same animals was achievable for only 12 to 24 h after ethyl parathion and for only 1 to 4 h after methyl parathion.